Alibaba Quote Change

I am making my first order on Alibaba. I have watched lot of videos and have an idea how to do things. I found 4 or 5 suppliers and sent them all an inquiry, and most got back to me right away. One of the supplier sent me a price of 200 for the units and 75 for the shipping fee. After I got back to them and told them to go ahead with the order, they sent me an invoice asking for 281. The price of the units was still 200, but the price of shipping has gone up from 75 to 81. I'm just wondering if this is normal and the price can fluctuate based off what their actual shipping cost is, or if I should request they stick with the original quote of 275. Thanks for the help.